In rotating the rolling bearing incorporating the resin-made cage at a high speed, a centrifugal force generated owing to a high-speed rotation acts on a cage. As a result, the cage deforms. Owing to the deformation of the cage, the friction between the cage and balls held by the cage becomes high, which leads to an increase in the torque of the rolling bearing. An increase in the friction therebetween causes the bearing to generate heat. Further as a result of the deformation of the cage, the cage may contact an outer ring of the rolling bearing. Resin melts owing to frictional heat caused by the contact between the cage and the outer ring. As a result, there may be a case where the rolling bearing is prevented from rotating. Thus the resin-made cage to be incorporated in the rolling bearing which is used at a high-speed rotation is demanded not to be deformed by a mechanical and/or thermal stress.
To restrain the deformation of the resin-made cage for the rolling bearing which rotates at a high speed, it is necessary to increase the mechanical strength such as the modulus of elasticity of a resin composition to be molded into the cage. To this end, normally this requirement is dealt with by allowing the resin composition to contain a large amount of a fibrous reinforcing material such as glass fibers. For example, as materials of the resin-made cage for the rolling bearing, from the standpoint of securing the strength and heat resistance of the cage, a material composed of polyamide 66 (hereinafter referred to as PA66) resin or polyamide 6 (hereinafter referred to as PA6) and glass fibers added thereto is known (see patent document 1). A plastic seal containing the PA66 resin or the PA6 resin is also known (see patent documents 2 and 3).
Because synthetic resins such as the PA6 and the PA66 are formed by way of synthesis of monomers extracted from petroleum and a polymerization reaction thereof, carbon dioxide is exhausted when the synthetic resins are burnt to discard it for a thermal recycle. From life cycle assessment (LCA), a comprehensive measure for decreasing the exhaust amount of the carbon dioxide is demanded in the production of materials, injection molding, and the discard of products. Thus the use of resin materials consisting of plant-derived materials is proposed. Cases in which plant resins such as polylactic acid, polytrimethylene terephthalate (hereinafter referred to as PTT) resin, and polyamide 11 (hereinafter referred to as PA11) resin are applied to the rolling bearing are reported (see patent documents 4 and 5).
Regarding the deformation of the resin-made cage and that of the resin-made seal, in addition to the deformation thereof owing to a mechanical or thermal stress caused by the rotation of the rolling bearing, the resin-made cage and the resin-made seal deform owing to swelling and expansion caused by moisture absorption made by the resin itself. The rolling bearing is used in a wide range of fields such as home electrical appliance, cars, various industrial equipments, and the like. In dependence on a use, the rolling bearing is often used in an environment where it is exposed to rainwater, in an environment where rainwater penetrates thereinto, in an environment where humidity becomes high, and the like. It is necessary to select a material which is unlikely to be affected by humidity for the resin-made member, for the rolling bearing, which is used in the environment where it is affected by humidity.